No it is not universal at all. For example, some materials are transparent, kind of like glass for light, another well known EM wave. You have to look up mater

No it is not universal at all. For example, some materials are transparent, kind of like glass for light, another well known EM wave. You have to look up materials frequency response: on earth, for example, athmosphere does not have a monotonous response (look at http://www.gb.nrao.edu/GBTopsdocs/primer/spect002.gif http://www.gb.nrao.edu/GBTopsdocs/primer/spect002.gif for example). Same with water: https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... Really, WiFi 5GHz is just well absorbed by walls and buildings, that's all.